Continuous-casting method



United States Patent 72] Inventor Irving Rossl Morristown, New Jersey[21] Appl. No. 693,430

[22] Filed Dec. 26, 1967 p [45] Patented Nov. 24, I970 [73] AssigneeCoocast Incorporated New Yorl New York [54] CONTINUOUS-CASTING METHOD 2Claims, 1 Drawing Fig.

[52] U.S. Cl. 164/82, 164/282 [51] Int. Cl. 822d 11/12 [50] Field ofSearch 164/82, 89, 273, 282, 283

[5 6] References Cited UNITED STATES PATENTS 2,698,467 1/1955 Tarquineeetal 164/89 3,257,691 6/1966 Krueger 164/282X 3,346,036 10/1967 Tarmann.l64/282X 3,344,841 10/1967 Rys Primary Examiner-J. Howard Flint, .lr.Assistant Examiner-R. Spencer Annear A trorney Sandoe, Neill, Schottler& Wikstrom ABSTRACT: In a continuous casting method wherein a strand ofmetal having a solidified skin and a molten core is formed in a chillmold and emerges from the lower end of the mold to be conducted along acurved guide path and is then straightened along a horizontal guidepath, the movement of the strand from the mold to the horizontal guidepath is controlled by driven rolls engaging the strand at a positionclose to the mold at the upstream end of the curved path, therebyavoiding Iongitudinal tension on the strand. In addition, the portion ofthe strand travelling from the mold to the horizontal guide path ismaintained in a temperature range such that the core remains molten andthe strand is sufficiently pliable to straighten out along thehorizontal guide path by its own weight.

Patented Nov. 24, 1970 INVENTOR IRVING ROSSI r CONTINUOUS-CASTING METHODcooled) which solidifies the periphery of the metal in the mold to forma strand having a solidified skin and a still molten core. The strandemerges from the lower end of the mold and is further cooled to completesolidification after which it is worked and/or cut into desired lengths.Additional molten metal is continuously poured in the upper-end'of themold to replace the metal withdrawn in the strand during a casting run.During casting, the mold is usually oscillated generally along its axisto facilitate mold release andto increase casting rate.

In conventional continuous casting machines the strand emerges from thelower, exit, end of the mold in a downward direction. It is known toconduct the strand along a'curved guide path from the mold and thenstraighten the strand to travel in a horizontal path in order to reducethe height of the apparatus required, and to cut, or otherwise work, thestrand in a horizontal position, which is more economical and convenientthan a vertical position. It is also known to use a curved mold to castthe strand in a curve compatible with the curved path it follows fromthe mold, and the curved molds are customarily oscillated in an arccorresponding to the radius of curvature of the mold or the path.

In accordance with conventional practice, the strand is withdrawn fromthe mold by withdrawal rolls engaging aportion of the strand which iscompletely or almost completely solidified, because it has been feltthat considerable pressure must be applied to draw the strand out of themold and to move it far enough along a curved guide path past a sequenceof cooling devices for it to be solidified sufficiently so as not to bedistorted by the pressure applied by the withdrawal rolls. It istherefore conventional practice to apply cooling devices,

such as water sprays, to complete solidification of the strand as ittravels along the curved guide path so that solidification is complete,or substantially complete, when the strand reaches the desiredhorizontal guide path. The withdrawal rolls are thus customarily locatedalong the first portion of the horizontal guide path orat the lower endof the curved guide path. With this arrangement, the casting speed islimited to the rate at which the strand can be sufficiently solidifiedto withstand the pressure of conventional withdrawal rolls, withoutbeing distorted by them, when the strand reaches the rolls. In addition,the use of withdrawal rolls in the conventional manner applies tensionto the newly formed portion of the strand which is only partiallysolidified. This tension is thus apt to break the strand or to produceundesired stresses and strains in it.

A further disadvantage of conventional methods and apparatus forwithdrawing the strand from the mold isthat solidification of the strandhas progressed so far when the su fficient'depending on the degree towhich friction is reduced along the-guide path which conducts the stranddown and away from the mold--to draw the strand out of the mold, withperhaps the application of some additional moving force. In any event,even if the lubrication on the surfaces of the mold and on the structureof the guide path away from the mold were such that the strand wouldmove out of, and away from, the mold due entirely to gravity, it wouldstill be desirable to apply some external moving force to control theemergence of the strand and stabilize the speed of withdrawal at auniformrate compatible with the casting operation of the 'mold and withthe most effective operating rates for subsequent apparatus performingwork on the strand.

It is therefore an object of the present invention to provide a castingmethod in which the emergence of the strand from the mold is controlledwithout applying longitudinal tension to the strand thereby avoiding thecreation of stresses and strains in the strand as it is conducted fromthe mold along a curved guide path to a horizontal guide path.

Another object is to provide a method in which the strand isstraightened onto a horizontal guide path without having to applyexternal straightening forces, which would tend to produce undesiredstresses and strains in the strand.

Still another object is to provide a method which enables a strand to becast at higher speeds than by conventional methods or with conventionalapparatus.

A further object is to provide a casting method which can be performedwith simpler, less expensive apparatus than conventional methods.

In accordance with the method of the present invention a control force,suitably a pair of driven rolls, is applied to the strand close to thepoint at which it emerges from the mold, to assure the movement of thestrand down a curved guide path to a horizontal guide'path. As mentionedabove, the force necessary to remove the strand from the mold andconduct it down a curved guide path has been overestimated in the art.Consequently, the pressure of the control force on the strand may bemuch less than the pressure applied by conventional withdrawal rolls andcan be applied to the strand, almost as soon as it emerges from the moldand while the skin around the molten core is relatively thin, withoutpermanently damaging or appreciably distorting the strand.

Further, in accordance with the method of this invention, the strandtravelling down the curved guide path to the horizontal guide path iscooled to the extent necessary to keep the skin from being remelted bythe core but not enough to solidify the'coreto an extent that the strandbecomes rigid. Thus, when the strand reaches the horizontal guide pathit is relatively limp and straightens out along the horizontal guidepath by its own weight, after which it is further cooled to completesolidification. In this way the sue of expensive As shown, molten metalfrom a conventional source, in-

dicated by the outlet 10 of a tundish, is poured in the upper end of aconventional continuously cooled, open ended chill mold 11, in which theperiphery of the metal iscooled to form a strand 12 having a solidifiedskin 12a and a molten core 12b. The mold 11 may have either a straightor curved mold cavity and in either case may be oscillated as in knowncontinuous casting apparatus. As indicated in the drawing, the peripheryof the metal, forming the skin 12a of the strand in the mold, shrinksaway from the walls of the mold. The strand 12 then emerges from thelower, exit, end of the mold, which is suitably provided with guiderolls 13 at opposite edges to guide the strand out the end of the mold.

.In accordance with the invention a control force, suitably providedby apair .of driven control rolls 14 hearing against opposite sides of thestrand 12, is applied at a position close to the exit end of themold andbetween the exit end and the upper portion of a curved guide path 15 forthe strand. As

' mentioned above, the force forwithdrawing the strand from the mold maybe considerably less than heretofore believed necessary. Consequently,the control rolls 14 operate with a relatively. light pressure on thestrand so as not to distort it, the portion of the strand at the controlrolls 14 having a molten core 12b within the solidified skin. Thepurpose of the control rolls 14 is twofold: one, toapply to the strand12 whatever slight degree of force may be necessary to assist itsmovement out of the mold, and two, to ensure that the strand moves outof the mold 11 and down the curved guide path 15 uniformly at a desiredrate. Cooling means, such as water sprays (not shown) may be applied tothe surface of the strand 12 between the exit end of the mold and thecontrol rolls 14.

The curved guide path 15 conducts the strand 12 from a point below themold to a horizontal guide path 16. The curved guide path may be formedin any suitable manner for supporting and guiding the strand and forpermitting the portion of the strand travelling along it to be cooled tosome extent. For example, the guide path 16 may be formed of a sequenceof idler rolls with water sprays for cooling arranged between the rollsand at opposite sides of the strand in a known manner for cooling thestrand, or by a single or seg-- mented chute having cooling meansincorporated therein or having spaces or openings with cooling devices,such as sprays or cooled surfaces, arranged therein. The horizontalguide path 16 may be similarly constituted, or may be formed in anyother suitable or conventional manner for guiding, supporting andcooling the strand.

In accordance with the invention, whatever means is applied to cool theportion of the strand travelling from the mold 11 along the curved guidepath 15 to the horizontal guide path 16, is applied to a degree to keepthe skin 12a from being remelted by the heat of the molten core 12b butnot enough to increase the thickness of the solidified skin, andcorrespondingly reduce the dimensions of the molten core, to an extentthat the strand becomes rigid. As indicated in the drawing a liquid coreis maintained in the strand (by limited exterior cooling) down to aportion of the strand which is on the horizontal guide path 16. Thus,the strand is maintained in sufficiently limp flexible condition tostraighten out by its own weight as it moves onto the horizontal guidepath 16, so that no additional, external straightening force isrequired.

In known apparatus, the strand may travel a considerable distance alonga horizontal guide path 16-to'carry the strand in contact with furthercooling devices, through annealing or temperature equalizing chambers,through shaping rolls, and/or in contact with cleaning devices, to acutting station, for exampleso that additional force may have to beapplied to continue the movement of the strand. In the drawing,

means for supplying this supplemental moving force is illustrated bydriven forwarding roll 17 engaging the strand 12 at a position along thehorizontal guide path 16. In this instance the forwarding roll 17 merelyserves to continue the movement of the strand further downstream, themovement of the strand from the mold 11 to at least the first portion ofthe horizontal guide path 16 being produced by a combination of gravityand the force applied by the control rolls 14.

It is to be understood that the embodiment of the invention shown in thedrawing and described in detail above is illustrative only and thatmodifications and variations may be made in the structure and mode ofoperation thereof without departing from the scope of the inventiondefined by the following claims.

I claim:

1. In a method of casting a strand of metal wherein molten metal ispoured in the upper end of an open ended chill mold which cools theperiphery of the metal therein to form a strand having a solidified skinand a still molten core and the strand emerging from the lower end ofthe mold is conducted along a curved guide path and is then straightenedalong a horizontal guide path, the improvement comprising, applyingdrive means to the periphery of the strand at a point between the lowerend of the mold and the upstream portion of said curved guide path forcontrolling the rate at which the strand moves along said paths, pushingthe strand along said curved guide path by applying a combination ofgravity and of the force applied by said drive thereby to reducelongitudinal tension and lateral'pressure on the strand, and maintaininthe periphery of the portion of the strand travelling from t e mold tothe horizontal guide path .within a temperature range for maintainingthe shell in solidified condition without completely solidifying thecore until said portion of the strand is in said horizontal guide pathwhereby said portion of the strand is sufficiently pliable tosubstantially straighten out along the horizontal guide path by its ownweight.

2. The method of claim 1 in which forwarding means is applied to theperiphery of the strand at a position along the horizontal guide pathfor moving the strand along the horizontal guide path beyond saidposition without applying appreciable withdrawal force on the portion ofthe strand travelling from the mold to the horizontal support path,whereby the speed of movement of the strand to the horizontal supportpath is substantially controlled by said drive means.

